1. Field of the Invention
The present invention relates to a light source apparatus and a projector using the same.
2. Description of the Related Art
Light source apparatuses are being used as light sources of various apparatuses such as illumination apparatuses and image projectors. Such light source apparatuses use fluorescent substance. The fluorescent substance absorbs (is excited by) excitation light emitted from an excitation light source to emit light of a wavelength different from the wavelength of the excitation light. Generally, light emitting diodes (LED) and laser diodes serving as semiconductor light sources are widely used as the light sources of such light source apparatuses. The fluorescent substance is dispersed into a transparent silicone resin layer or an epoxy resin layer to be formed as a light emitting layer.
However, a resin binder used for a light-emitting layer deteriorates due to excitation light from the semiconductor light source, or is broken when the excitation light has particularly high intensity. In addition, low thermal conductivity of resin causes an increase in temperature of the fluorescent substance dispersed into the resin, and the increase in temperature causes a phenomenon such as shift in wavelength of the light emitted from the fluorescent substance, or temperature quenching that decreases the light emission intensity, and consequently causes the problem of decrease in brightness of the light source apparatus.
To reduce such damage and effects caused by heat, known is a method of arranging fluorescent substance in a large area to prevent continuous application of excitation light to the same part. For example, as disclosed in Jpn. Pat. Appln. KOKAI Pub. No. 2011-13316, a resin binder containing fluorescent substance is concentrically applied onto the surface of a disk, to rotate the disk by a motor or the like in use.
However, this method produces a structure in which a fluorescent substance-containing resin layer continues in the rotational direction of the disk. Consequently, light emitted from the fluorescent substance is reflected and transmitted inside the fluorescent substance-containing resin layer, and light is emitted outside the range of a condensing lens that is positioned to condense light emitted from fluorescent substance. This phenomenon obstructs effective use of light emitted from fluorescent substance, and wastes the light.
In recent years, as means for improving heat resistance of light emitting layers including dispersed fluorescent substance, it is presented to use a translucent inorganic material such as glass, instead of a transparent resin binder, or use ceramics having high thermal conductivity as disclosed in Jpn. Pat. Appln. KOKAI Pub. No. 2006-282447, to form light emitting layers (such light emitting layers will be referred to as fluorescent substance plates hereinafter). In particular, fluorescent substance plates using a translucent ceramics binder have thermal conductivity dozens to hundreds of times higher than the thermal conductivity of light emitting layers using a conventional resin binder, and have markedly improved heat dissipation.
FIG. 8A is a diagram illustrating an outline of an excitation optical structure that is supposed in the case of applying a fluorescent substance plate 100 using a translucent ceramics binder to a light source apparatus. Excitation light 102 from an excitation light source 101 such as a semiconductor laser passes through a collimator lens 103, and a dichroic mirror 104 that transmits the wavelength of the excitation light 102, and is condensed to a desired size of irradiation range of the fluorescent substance plate 100 by a condensing lens group 105. The fluorescent substance emission light emitted from the fluorescent substance plate 100 is condensed by the condensing lens group 105 to the dichroic mirror 104 as fluorescent substance effective emission light 106. Light of a desired wavelength band is taken out by the dichroic mirror 104, and used as illumination light.
FIG. 8B is a diagram illustrating an excitation light irradiation region 107 serving as an irradiation range of the excitation light 102 for the fluorescent substance plate 100. In the present specification, the excitation light irradiation range 107 indicates a range in which the energy intensity of the excitation light 102 is 10% (to 20%) or more of the maximum intensity thereof.
The fluorescent substance plate 100 is formed to have a rectangular shape having side lengths of Ax and Ay. The optical system is designed such that the excitation light irradiation range 107 serves as a rectangular region on the rectangular fluorescent substance plate 100 and side lengths Ex and By of the excitation light irradiation region 107 are slightly smaller than the side length Ax and Ay, respectively, of the fluorescent substance plate 100. Specifically, the condensing lens group 105 condenses the excitation light 102 from the excitation light source 101 to the excitation light irradiation region 107 of the fluorescent substance plate 100. The condensing lens group 105 is designed to take in the fluorescent substance emission light from the excitation light irradiation region 107 to a desired angle to be used as fluorescent substance effective emission light 106.
A light source having a smaller light emission size is more preferable, and the lengths Bx and By of the excitation light irradiation region 107 should be smaller to improve the optical efficiency. However, the fluorescent substance plate 100 to match them has a finer size, and becomes difficult to manufacture in terms of handling in mounting, and incurs an increase in cost.
For this reason, the lengths Ax an Ay of the fluorescent substance plate 100 should be set sufficiently larger than the lengths Bx and By of the excitation light irradiation region 107. In the case of increasing the lengths Ax and Ay of the fluorescent substance plate 100 as described above, because fluorescent substance emission light is emitted in all directions from activated elements that emit light inside the fluorescent substance, the fluorescent substance emission light is emitted from a position of a fluorescent substance plate upper surface 100U that is widely distant from the excitation light irradiation region 107, as illustrated in FIG. 80. Specifically, because the fluorescent substance plate 100 is generally placed on a substrate (not illustrated), a fluorescent substance plate bottom surface 100B has an optical total reflection property, and fluorescent substance plate side surfaces 100S serving as cut portions have such total reflection property to a certain degree. With this structure, the fluorescent substance emission light that is emitted from the excitation light irradiation region 107 in all directions is transmitted through the inside of the fluorescent substance plate 100, totally reflected by the fluorescent substance plate bottom surface 100B or the fluorescent substance plate side surfaces 100S, and easily outgoes from the position of the fluorescent substance plate upper surface 100U that is widely distant from the excitation light irradiation region 107. The emission light that outgoes from the position that is widely distant from the excitation light irradiation region 107 serves as fluorescent substance ineffective emission light 108 existing outside the taking range of the condensing lens group 105, and is not effectively used. Otherwise, the reflection optical path of the emitted light inside the fluorescent substance plate 100 becomes long, and the emitted light is self-absorbed into the activated elements, to cause the phenomenon of loss of the emitted light.
An object of the present invention is to provide a light source apparatus capable of reducing loss of emitted light, and a projector using the same.